The state said Monday it is continuing to investigate a surge in fraudulent tax returns submitted online through TurboTax, while the company behind the do-it-yourself tax preparation software conducts its own investigation.

TurboTax parent company Intuit stopped processing state returns for about 24 hours last week after Alabama and other states reported a spike in filings with stolen personal information. Intuit spokeswoman Julie Miller said most victims found out when they tried to file their returns and were rejected because someone else had already filed in their name.

The company resumed filing of state returns at 5 p.m. Friday with increased anti-fraud measures. Intuit has been working with third-party security company Palantir to investigate the problem.

"Based on that examination, Intuit believes that these instances of fraud did not result from a security breach of its systems," Miller said. "Given we continuously monitor our systems, this work is ongoing."

Miller said Intuit has now implemented security measures targeting this type of fraud, including multi-factor authentication.

The Alabama Department of Revenue said it has flagged more than 16,000 returns as possibly fraudulent, but ADOR spokesman Frank Miles said Monday that the state doesn't yet have a total for the number of confirmed fraudulent returns. The state is reaching out to victims individually to let them know their identities may have been compromised.

"The department's investigation is ongoing, and we continue to check all returns for fraudulent activity," Miles said.

ADOR said its own electronic data remains secure and has not been compromised.

TurboTax processed 30 million tax returns last year, the company said.

There haven't been issues with federal returns to date because the Internal Revenue Service has implemented stronger fraud detection policies, Miller said.

The IRS issued a statement Monday noting that they "remain in close contact" with the software industry and state tax administrators. The IRS said it has added and strengthened protections in its filing system.

"Taxpayers should continue to file their tax returns as they normally would," the statement said.

Alabamians who who want to check on the status of their state returns can visit myalabamataxes.alabama.gov or call 242-1170.

The Associated Press contributed to this story.

At a glance

Alabama has flagged 16,000 state returns as possibly fraudulent after a burst of false filings through TurboTax

Most victims find out when they try to file a state return and are rejected because someone else has already filed under their names

The state is notifying victims individually while continuing to investigate and says its internal data is secure